This application addresses broad Challenge Area (05) Comparative Effectiveness Research (CER) and specific Challenge Topic, 05-LM-103: Improving Compliance of School Children with Immunization Schedules. Despite the immense success of the immunization program in this country, in 2007 approximately 25% of children had not received all recommended vaccines before kindergarten. Lower vaccination rates are especially prevalent among poor and minority children who may not have a usual site of primary care. In addition to receiving all recommended vaccines, the need to receive vaccines in a timely manner is also important, given the particular vulnerability of young children to a host of vaccine-preventable diseases. For these reasons, one of the nation's major health priorities, as outlined in Healthy People 2010, is to increase the proportion of children aged 19 to 35 months who have received all universally recommended vaccines. The Task Force on Community Preventive Services has recommended several evidence-based interventions to increase immunization coverage, including parent education and patient reminder/recall for immunizations. Although such efforts have been shown to be effective when used at the practice level, they remain underutilized by most providers because of the burdens and competing demands in primary care practice. The current proposal compares the effectiveness of standard approaches to raising immunizations at the practice level to an innovative approach to recalling children age 19-35 months who are behind on immunizations and to educating families that do not rely on practice-based efforts, but rather focused efforts at the level of the community. It is hypothesized that a population-based approach may reduce the burdens on primary care providers and increase the capacity to reach and immunize children who do not have a usual source of primary care. The study builds upon the extensive experience of the study team in conducting immunization delivery research within practice, public health and community settings and will be conducted in conjunction with the Colorado Immunization Information System and local county public health departments throughout the state. The proposed study will be a group-randomized trial at the level of the county comparing two approaches to improving immunization rates in young children in both urban and rural areas. The first approach will involve the implementation of standard evidence-based methods at the level of individual primary care practices and the other will use innovative technologies, including the ongoing population of the Colorado Immunization Information System with birth certificate data and centralized recall of patients at the level of the county. The study will be conducted in six primarily urban counties and eight primarily rural counties. The effectiveness of each type of intervention at increasing immunization rates will be compared as well as the feasibility and cost of each approach. Finally, a qualitative component will assess the acceptability of the two approaches to providers and patients and will assess barriers to the success of each. Results of this study will help direct future national efforts to increase up-to-date rates in young children prior to school entry. One of the nation's major health priorities, as outlined in Healthy People 2010, is to increase the proportion of children aged 19 to 35 months who have received all universally recommended vaccines. This study will compare two interventions for increasing immunization rates in this age group, one using well-studied primary care practice-based methods and the other using innovative technologies to increase immunization rates at the population-level. Results of this study will provide data that will be relevant nationally in guiding future investment of resources to increase up-to-date rates in young children prior to school entry.